Background technology of an AC voltage regulator is that two semiconductor elements (such as, thyristors, hereinafter using thyristor as semiconductor elements) are connected in an AC circuitry in series after connected in anti-parallel, and AC output may be controlled by controlling the thyristors or other power electronic components. This circuit, which does not change the frequency of alternating current, is termed as an alternating current control circuit. The single/three-phase circuitry constituted by the control circuit is an AC voltage regulator. That is, a control device constituted by the semiconductor elements for converting an alternating current into another alternating current with the same frequency and different voltages.
Background technology of a transformer switch is that the voltage regulation is performed on transformer in voltage in order to supply stable voltage through the power grid, and control the current flow or regulate the load current. At present, the method for voltage regulation on transformer is a stepped voltage regulation method which is performed by disposing tap switch on the coil at one side thereof, so as to increase or decrease wire turns, achieving the for changing voltage ratio. Such a circuitry for regulating voltage by coil tap is termed as a voltage regulating circuit. The component for changing tap to regulate voltage is termed as a tap switch. The voltage regulating in which the secondary winding applied with no load and the primary winding disconnected with the power grid is termed as a non-excitation voltage regulating, and the voltage regulating applied with a load for changing coil tap is termed as an on-load voltage regulating. Consequently, the transformer switch is classified into two types, namely, a non-excitation tap switch, and a loaded switch. The insulation level of the loaded switch is determined by the max ground potential of the voltage regulating coil under a surge voltage, and total insulation is determined by the shock gradient of the voltage regulating coil under a surge voltage. As the level of insulation and the offset voltage are high, the switching capacitor discharges.
Background technology of a conventional series voltage regulating transformer is that, in low-voltage and high-current system application, the series voltage regulating transformer is constituted by two transformers, one for main transformer (constant at low voltage side), and another for series voltage regulating transformer (adjustable at low voltage side). A single voltage regulating winding provided on the main transformer is required for supplying power to series high voltage side. The low-voltage windings of main and series transformers are connected together in series and utilize a splayed coil structure, the voltage of low voltage windings of main transformer are constant, and the voltage of low voltage windings of series transformer are adjustable, so that the voltage of the two serially coupled low voltage windings are changed, thereby changing the synthetic voltage of the two low voltage windings. The main transformer comprises a high voltage winding, a low voltage winding, and a voltage regulating winding. The series transformer comprises a high voltage winding and a low voltage winding which are used in low-voltage and high-current system application.
Background technology of high voltage or ultra-high voltage AC power transmission system is that: the ultra-high voltage power transmission system is a new power transmission method for transmitting greater power to further distance than 500 KV AC power transmission method. It includes AC ultra-high voltage (UHV) and high voltage direct current (HVDC), and has the following advantages: cheap transmission costs, simple power grid structure, small short-circuit current, less transmission corridors occupation and improved power supply quality, etc. AC ultra voltage represents for a voltage higher than 1000 kV as defined by the International Electrotechnical Commission. In China, the ultra voltage represents for 1000 kV or more AC power, or 800 kV or more DC power. UHV AC transmission has disadvantages of higher voltage, long transmission lines, large distribution capacity, small wave impedance, obvious fault wave process. Even though the UHV transmission lines are typically mounted with paralleling reactor so as to compensate charge current of transmission lines, and suppress the occurrence of overvoltage, as well as decrease transmission capacity of the transmission lines, which is opposite to the fundamental purpose of UHV power transmission.
The main advantages for utilizing high voltage or ultra-high voltage AC power transmission is as follows: (1) improved transmission capacity and transmission distance; (2) improved economical efficiency for power transmission, wherein higher power transmission voltage means cheaper transmission capacity per unit; (3) saved floor space of the corridors for transmission and floor space for transformer substation; (4) reduced power loss for transmission line; (5) convenience for networking, simplified network topography, decreased failure rate.
Background technology of high voltage DC power transmission system: with development of power electronic technology, DC high-voltage power transmission becomes feasible, and is possible to become fully effective in all its aspects. At present, almost over 80 high voltage DC power transmission projects have been put into operation all over the world. In China, more than 10 high voltage DC power transmission projects are utilized in the national electricity grid, which play an important role in optimizing energy configuration, guaranteeing national energy security, and promoting national economic development. With the implementation of the Chinese national strategic guidelines, such as, “Western Power to the East, North and South to Share Power, National-link Network”, it has become a tendency to accelerate the construction of millions volts level of AC and ±660 kV, ±800 kV, ±1000 kV level of DC system UHV power grid as a centre power grid architecture. The concept of high voltage DC power transmission is a way of power transmission that the AC power generated by power plants is changed into DC power by rectifiers to be transmitted to receiving ends, and is changed into AC power by inverters to be transmitted to receiving ends. This way of transmission is mainly utilized in long-distance and high-power power transmission and networking of networking of nonsynchronous AC systems, has lower transmission line costs in economy, and lower power loss per year.
There are lots of advantages of DC power transmission in technology, firstly, the problem of system stability does not exist, and nonsynchronous interconnection in the power grid may be possible, while in the AC power system, the entire synchronous generator in the AC power system keep synchronized. The transmission capacity and distance in DC power transmission are not influenced by stability of synchronized operation, and may be connected to two systems with different frequencies, thereby achieving nonsynchronous networking and improving stability of the system. Secondly, the DC power transmission has limit on short-circuit current. If the AC power transmission line is used for connecting two AC systems, the capacity of short circuit is increased, and even a circuitry breaker is required to be replaced or a current-limiting device is required to be added. However, when the DC power transmission line is used for connecting two AC systems, the “constant current control” of the DC system limits the short-circuit current near rated power, and thus the capacity of short circuit is not increased due to interconnection. Moreover, the regulation is very fast, and operation thereof is reliable. The DC power transmission may rapidly adjust the active power through silicon controlled rectifier converters to achieve “current tipping” (change of flow direction of the power). In DC power transmission, under normal condition, stable output is ensured. When a failure is occurred, urgent support to fault systems by sane systems is achieved, and suppression on oscillating damping and sub-synchronous oscillation may be achieved. When the AC/DC lines run in a manner of paralleling operation, if the AC transmission lines short out, the DC transmitting power may be increased briefly to decrease the acceleration of the rotor of the generator, thereby improving the reliability of the system. Thirdly, there is no capacitor charging current. Under steady state of the DC transmission line, there is no capacitance charging current, the following voltage is stable, and when there is no idle load or light load, abnormal incensement in voltage is observed at the AC long line-receiving end and mediate portion, and there is no need for connecting reactance in parallel to compensate. Furthermore, the floor space of the corridors is saved.
Background technology of electrochemically electrolytic system: in a electrochemical electrolytic system, the electrolytic current is required to maintain constant to ensure stability of the electrolysis bath thermal scheme and improvement of current efficiency, so as to relief labor intensity of the workers, and there is great advantage to reduce anode effect of aluminum electrolysis. If the electrolytic current is larger or smaller than rated value for a long time, then the thermal equilibrium in the electrolysis bath may be broken, so that the bath is overheated or subcooled to influence production and yield. The existing electrolytic silicon rectifier units are not silicon controlled units due to power factors, and barely provided with saturated reactor. And even it was provided, the units have small modulation range in view of economy. Those rectifier units without saturated reactor have power factors up to 0.94. Thus, the regulation of DC output voltage is mainly based on loaded tap switches in the transformer. However, the loaded tap switches have slow operation speed, and thus may not amend momentary fluctuation of the electrolytic current, such as, when anode effect occurs in aluminum electrolysis (depend on the difference line voltages, line current may be decreased by 5-10% which lasts for several minutes). If the tap switches are utilized for elevating voltage to maintain the series current, when the anode effect does not exist, current impact will occur due to lower operation speed of the tap switches. Thus, this transitory variation of current is typically not regulated. In addition, in order to reduce the times of operation for the loaded tap switches, it is impossible to respond to transitory variation of current. The operations of loaded voltage regulation switches are very frequent. There are at least 36000 times based on 100 times per switch each day, and the tap switches are required to be maintained once per 3000 times, which means long repair cycle, and has a strong impact on production. Thus, it is very important to reduce frequent operation of the loaded voltage regulation switch and prolong its service life. Thus, a constant current control scheme of rapid self-regulation which is turned off or on upon anode effect is typically not utilized in aluminum electrolysis, in order to reduce frequent operation of loaded tap switch, and the voltage fluctuation with time of duration less than 2 minutes causes frequent operation of loaded tap switch.
It is also very important to obtain a high-precision, long-life and high-speed current regulating system. In the field of electrolytic producing, yield is directly related to ampere-hour, and various process indexes are closely related to average current. In this case, it is desirable to obtain an automatic high-speed current stabilizer capable of maintaining the error of average current or ampere-hour less than 0.25% to 0.1% in several hours. However, it is very difficult to achieve the above accuracy only by utilizing the loaded tap switches in the system. The operations of the loaded tap switches are very slow with respect to the response for current modulation system. Typically, there is no response to variation of current within 10% lasting for several minutes, and there must be transient response to large variation of current exceeding normal range of operation. However, the variation time for voltage regulation of the loaded switch is 10 s to 20 s, when the range of voltage regulation is large, the response time will fail to follow up with the variation time of current.
Background technology of electric furnace smelting: the smelting process of electric furnace is divided into two processes, i.e., a melting period and a refining period. In the melting period, the cover is sealed and three-phase electrodes are connected after steel scrap is loaded. After the three-phase power is turned on, large-current arc is generated between the electrodes and the steel scrap, and the steel scrap is melt due to heat of the arc. Compared with the arc of the melting period, the arc in the refining period is relatively stable, the current is basically constant, and at this time, the voltage variability and flicker effect are exceedingly small.
Typically, the smelting period of AC arc furnace is about 1 h to 3 h, and the supplied voltage is 110 KV or 35 KV. When a specially designed arc furnace transformer is powered, the voltage between secondary side electrodes is typically between 100V to 700V, wherein the voltage drops of the electrodes are about 40V, the arc drop is about 12V/cm, and the longer the arc, the larger the voltage drop. The current control of arc furnaces is achieved by switch between taps of high-voltage side winding of the transformer of the arc furnace and regulation of electrode voltage, i.e., the furnace transformer defines a value for input arc voltage by using a switch, and three-phase graphite electrodes are controlled to insert into the furnace, and the lifting device of the electrodes is controlled to move up and down, the input power of the furnace is controlled, thereby controlling the arc current in the furnace. The arc furnace consumes large reactive power, and has a large variation. In the melting period, due to direct arc between steel scrap and electrodes, as the steel scrap melts, the length of the arc will certainly change, thereby causing movement of the arcing points, and the electrode controlling system cannot follow up with saltatory variation of the arc and cannot compensate timely due to mechanical inertia response time within several seconds to ten or more seconds, and thus the arc is not stable. At the beginning of the melting period, as the temperature in the furnace is lower, the arc is hard to be maintained, and is not stable frequently, and thus the current is discontinuous. In order to maintain the arc stable, the power factor of the arc furnace is not high, and sudden variation of the current will cause concurrent and sudden variation of the active power and reactive power extracted by the arc furnace from the power supply system, i.e., in the process of smelting in the arc furnace, the arc current is rapidly changed by a large margin. Since the electric arc furnace is a high inductive load, when the high-power arc furnace operates in melting period, the power factor is even lowered to 0.1 to 0.2, which causes serious fall in bus bar voltage. When voltage is reduced, and active power of the electric-arc furnace is decreased correspondingly, the molting period is prolonged, and the productivity is decreased. The power factor of the arc furnace is 0.1 to 0.2 when the electrode is shorted out, and is 0.7 to 0.85 under rated operation. As the melting proceeds, the electrode voltages are decreased, scrap is melted from the lower portion. After the lower scrap is melted, the upper part of the steel block fall down, causing sudden two-phase short-circuit of electrode ends, and thus the arc current will change sharply by a large margin. Variation of arc current causes sudden variation of voltage, and rapid variation of arc due to movement of arcing point is called period sudden variation, sharp variation caused by electrode short circuit is called abnormal sudden variation, which will cause serious voltage fluctuations and sudden variation on public buses of the power system. Meanwhile, the caused voltage fluctuations and sudden variation is very fierce. When the two-phase electrodes are shorted out, and one phase is open, the amplitude of variation of the current is the largest, and thus the caused voltage fluctuations and sudden variation is the largest. The arc furnace system is a strongly nonlinear system with a three-phase coupled feature, and its parameters are time-varying, and at the same time, are influenced by random perturbation. It is a world-wide puzzle for control engineers to adjust proper length of the arc and make it stable through an electrode regulation system. As for power saving in smelting steel by arc, power consumption per ton of steel is lowered by 1-2 kwh once the smelting time is shorted by 1 minutes, and it is effective to shorten the smelting period by using computers to control the smelting period of the arc furnace. In the melting period, the power consumption is over 60% of the whole smelting process, the power consumption is directly influenced by the power supply during the melting period, but the condition in the furnace during the melting period is complicated, which is accompanied by firing, penetration, short circuit, arc breaking, splatter, and evaporation, which cause unceasing variation of arc power and operation current. Under manual control, It is hard to achieve the objectives of lowering the temperature of the steel, reducing the waiting time for steel, stabilizing arc current, reducing the times of short circuit and breaking arc, shortening the melting period, lowering power consumption per ton of steel. However, the automatic control of the furnace is mainly control of voltage of the electrodes, and control of the input power, while the electrode controlling system consists of a hydraulic system, due to mechanical inertia, the regulation of the electrodes is slow in speed and weak in sensitivity, and cannot follow up with the sharp variation of the arc, and thus cannot compensate timely, which is the most hardest part. In the process of smelting period, the length of the three-phase electrodes should be changed with respect to the length of the arc, and regulated based on the relative distance between the electrodes and the raw materials, thereby ensuring the length of the arc stable to make best use of the arc to melt the furnace burden. As the controlled objects of the AC arc furnace in smelting has characteristics of highly nonlinear, strong coupling, time-dependent nature and time-lagging nature, in the process of melting, external perturbations are very obvious, and variation of arc length and deviation is large, which requires a electrode controller having a characteristic of relatively higher fast response without overshoot.
Background technology of electric locomotive traction: high-speed railways are system integration of innovative and high technology, and its construction and operation reflect the scientific and technological strength of a country. In May, 1985, the Economic Commission for Europe of the United Nations stipulated that passenger transport line with running speed over 300 km per hour and mixed passenger and freight line with running speed over 250 km per hour are high speed railways. The existing traction transformer mainly use non-excitation regulator, which has small range of voltage regulation. The traction transformer is used for transmitting the power of three-phase power supply system to two single-phase traction lines with loads respectively. The two single-phase traction lines are used for powering the uplink and downlink locomotives. In an ideal case, the two single-phase loads are the same. Thus, the traction transformer is used as a transformer for transforming three phases into two phases. The traction transformer is a power transformer of a special voltage class, should meet the requirement of fierce variation of traction load and frequent external short circuit, and thus is the “heart” of the traction substation. In China, the traction transformer is divided into three types, i.e., a three-phase, a three-phase to two-phase, and a single phase, and thus the traction substation is divided into three types, i.e., a three-phase, a three-phase to two-phase, and a single phase.
Background technology of voltage regulator: a voltage regulator is voltage regulating power source for supplying adjustable voltage to loads; it can convert the distribution voltage of the uncontrollable power grid; it can be used for any load voltage which may be regulated in a stepless manner in a certain range, and is divided into, based on the electromagnetism principle and structure, a contact voltage regulator, a induction regulator, a magnetic voltage regulator, a moving-coil regulator, a purification regulator (stabilizer), a saturated reactor, an auto regulator and the like.
The contact voltage regulator has a capacity of 0.1 to 1000 KVA, a voltage class of 0.5 KV, a range of voltage regulation of 0 to 100%. The induction voltage regulator has a capacity of 6.3 to 4500 KVA, a voltage class of below 10 KV, a range of voltage regulation of 5 to 100%. The magnetic voltage regulator has a capacity of 5 to 1000 KVA, a voltage class of below 0.5 KV, a range of voltage regulation of 15% to 100%. The moving-coil regulator has a capacity of 1000 to 2250 KVA, a voltage class of below 10 KV, a range of voltage regulation of 5 to 100%. The contact auto regulator has a capacity of 20 to 1000 KVA, a voltage class of 0.5 KV, a range of voltage regulation of ±20%. The induction auto regulator has a capacity of 20 to 5600 KVA, a voltage class of below 10 KV, a range of voltage regulation of ±20%. The purification stabilizer has a capacity of 1 to 300 KVA, a voltage class of 0.5 KV, a range of voltage regulation of ±25%. The thyristor voltage regulator has a capacity of below 450 KVA, and a voltage class of below 10 KV.
Background technology of reactive compensation: it is common knowledge of the designers and decision makers all over the world to use the reactive compensation technology to improve the power factor of a system, and the investment of the reactive compensation device has been listed in the integrated planning of electric power investment, which has become an indispensable link. At present, the power factor of the main power network equipment is on the order of 1, the law of Russia provide that the power factor should greater than 0.92, and Japan and other countries have established nationwide reactive power management committee to research technical economic policy about reactive compensation. Practically, almost all the developed countries have higher power factors of power grids. Thus, it is a tendency in power grid to greatly improve the power factors of power grids, lower line loss, save energy, and develop the capacity of power generation assemblies.